An electromagnetic interference suppressing body is used for suppressing electromagnetic interference caused by interference of undesired electromagnetic waves.
Conventionally, for blocking invasion of the external undesired electromagnetic waves into an electronic device, shielding of the electronic device by a conductor has been carried out. However, since the blocking of the electromagnetic waves by the conductor aims to reflect the electromagnetic waves, radiant waves from a certain component within the electronic device may be reflected to adversely affect other components in the same electronic device as secondary noise. Particularly, following reduction in size and increase in working frequency of electronic devices in recent years, problems of the interference due to the external electromagnetic waves and the secondary noise due to the internal electromagnetic waves are serious.
JP-A-7-212079 discloses a composite magnetic body which can suppress interference of undesired electromagnetic waves utilizing absorption of highfrequency waves due to a complex permeability of a soft magnetic body of a certain kind. This composite magnetic body is constituted of a composite magnetic sheet formed by mixing soft magnetic powder into an organic binding agent.
The sheet of the composite magnetic body may be used as it is. On the other hand, by forming a structure stacked with a conductive sheet, the coming electromagnetic waves are absorbed by the composite magnetic sheet and the electromagnetic waves passing through the composite magnetic sheet are reflected by the conductive sheet into the composite magnetic sheet, so as to suppress the interference of the undesired electromagnetic waves.
Such an electromagnetic interference suppressing body is disposed, for example, on the surface of an electronic device or around an electronic component in the electronic device which is liable to be adversely affected by external electromagnetic waves. Alternatively, it maybe used for positioning it between two printed circuit boards each having mounted thereon with electronic components confronting each other with a space therebetween.
Incidentally, the foregoing composite magnetic sheet has been produced by hot pressing a kneaded slurry material in the form of soft magnetic powder and an organic binding agent suspended and dispersed in an organic solvent.
A drawback with this method is that when the composite magnetic sheets are produced by the hot pressing, entrainment of the air into the composite magnetic sheets occurs, whereby the yield of acceptable composite magnetic sheets is adversely affected.
Further, since the method of hot pressing is a batch process, it is unsuitable for the mass production.
On the other hand, an absorption capacity of undesired electromagnetic waves of the composite magnetic body is determined by a thickness thereof assuming that a material to be used is the same.
Therefore, an object of the present invention is to provide method which for the mass production of composite magnetic sheets of a required thickness.
Another object of the present invention is to provide a method of producing a composite magnetic sheet of high-quality with less entrained air.
Further, another object of the present invention is to provide a method of producing a composite magnetic sheet which, in view of the shape thereof, reduces reflected components and transmitting components and improves the absorption rate of electromagnetic waves.
Another object of the present invention is to provide a method of producing an electromagnetic interference suppressing sheet having a stacked structure of composite magnetic sheets and a conductor layer resistant to mechanical exfoliation.